An excellent history of the stereoscope can be found in, "Foundations of the Stereoscopic Cinema: A Study in Depth," Lenny Lipton, Van Nostrand, Reinhold Company, New York, N.Y., pp. 21-28 (1982).
In this study, essentially two basic designs of the stereoscope are mentioned. The first, developed initially in 1833 by Wheatstone, required two diametrically opposed stereoscopically complementary images, one placed to the left of the left eye at a 90 degree angle to the line of sight and the other placed to the right of the right eye also at a 90 degree angle to the line of sight. The system required two mirrors, one for each eye/image and the mirrors reflected the right image to the right eye and the left image to the left eye.
The Wheatstone system, however, suffers from the disadvantage that two physically separate images are required to provide the stereoscopic effect and the disadvantage that the stereoscope was required to be relatively wide to accomodate the placement of the two images which must be outside of the observer's head.
In 1856, Brewster invented a lens based stereoscope which produced a stereoscopic image from two stereoscopically complementary images placed side by side directly in front of the observer. The Brewster system has some limitations including the requirement of special lenses to produce a stereoscopic effect, the need to place the images at the focal point of the lenses and to place the lenses at a particular distance from the observer.
Most of the patented stereoscopes are of the Brewster type employing side by side images and a lens system. Examples of variations on this system can be found in U.S. Pat. Nos. 2,511,334 and 3,850,505 and others which disclose the Viewmaster.TM. type devices, book viewing devices such as are found in U.S. Pat. Nos. 40,654; 472,196; 2,616,333 and 2,683,391; and foldable/mailable 3-D viewers for viewing from side by side post card images such as is disclosed in U.S. Pat. No. 5,136,423.
In addition, in recent patent literature such as U.S. Pat. Nos. 4,998,799, one finds a special device for viewing two stereoscopically complementary images which are positioned one above the other. This device has the advantages of not requiring adjustments to compensate for eye spacing, and the capability of using two photographs taken by a conventional camera to create a three dimensional image.
Further, U.S. Pat. No. 4,.561,723 discloses an electronic stereoscopic viewing device whereby two side by side electronically generated images are employed to create a stereoscopic effect with the aid of a combined lens and mirror system.
It is the primary object of the present invention to provide a stereoscopic viewing device which can be used to create a stereoscopic image from back to back stereoscopically complementary images.
It is a second object of the present invention to provide a stereoscopic viewing device which can create a stereoscopic image from a single card bearing two stereoscopically complementary images which can be arranged back to back In relation to one another.
It is a third object of the present invention to provide a novel card which bears two stereoscopically complementary images in a manner such that said images can be arranged back to back for viewing with the device of the invention.
It is a fourth object of the present invention to provide a portable stereoscopic viewing device which can create a stereoscopic image from two stereoscopically complementary images arranged back to back.
These and other objects of the present invention will be apparent to a man of ordinary skill in the art from the description and drawings which follow.